Imidazo[1,2-α]pyridines possess adenosine A1 receptor affinity for the potential treatment of cognition in neurological disorders.

Previous research has shown that bicyclic 6:5-fused heteroaromatic compounds with two N-atoms have variable degrees of adenosine A1 receptor antagonistic activity. Prompted by this imidazo[1,2-α]pyridine analogues were synthesized and evaluated for their adenosine A1 and A2A receptor affinity via radioligand binding studies and subjected to a GTP shift assay to determine its adenosine A1 receptor agonistic or antagonistic functionality. Imidazo[1,2-α]pyridine, the parent scaffold, was found devoid of affinity for the adenosine A1 and A2A receptors. The influence of substitution on position C2 showed no improvement for either adenosine A1 or A2A receptor affinity. The addition of an amino or a cyclohexylamino group to position C3 also showed no improvement of adenosine A1 or A2A receptor affinity. Surprisingly para-substitution on the phenyl ring at position C2 in combination with a cyclohexylamino group at position C3 led to adenosine A1 receptor affinity in the low micromolar range with compound 4d showing: (1) the highest affinity for the adenosine A1 receptor with a Ki value of 2.06µM and (2) adenosine A1 receptor antagonistic properties. This pilot study concludes that para-substituted 3-cyclohexylamino-2-phenyl-imidazo[1,2-α]pyridine analogues represent an interesting scaffold to investigate further structure-activity relationships in the design of novel imidazo[1,2-α]pyridine-based adenosine A1 receptor antagonists for the treatment of neurodegenerative disorders.

Caspase-3 activation and induction of PARP cleavage by cyclic dipeptide cyclo(Phe-Pro) in HT-29 cells.

BACKGROUND: Cyclo(Phe-Pro) has been shown to inhibit cancer cell growth and induce apoptosis in HT-29 colon cancer cells. MATERIALS AND METHODS: The molecular mechanisms mediating cyclo(Phe-Pro)-induced apoptosis in HT-29 cells were investigated. Cells were treated with 5 mM or 10 mM cyclo(Phe-Pro) for varying times. Immunoblot analysis was used to detect poly(ADP-ribose)polymerase (PARP) cleavage. A fluorescence-based enzymatic assay was used to measure caspase-3 activity. RESULTS: Cyclo(Phe-Pro) (10 mM) induced time-dependent cleavage of PARP, detected as early as 8 hours post treatment. PARP cleavage was blocked by co-administration with the broad-range caspase inhibitor Z-VAD-FMK Cyclo(Phe-Pro) also induced a time-dependent increase (p < 0.01) in caspase-3 activity. This increase in activity was blocked in the presence of the caspase-3 inhibitor Ac-DEVD-CHO. CONCLUSION: These results provide evidence that cyclo(Phe-Pro)-induced apoptosis in HT-29 cells is mediated by a caspase cascade. These findings warrant further investigation into the potential antitumour activity of cyclo(Phe-Pro) and its related cyclic dipeptide derivatives.

Comparison of the structure of key variants of microcystin to vasopressin.

Microcystins (MCs) are cyclic heptapeptide compounds [where X(2) (position 2) and Z(4) (position 4) are variable l-aminoacids] produced by cyanobacteria and responsible for severe liver damage in animals ingesting acute doses of the toxic compounds. Certain variants of microcystins are more toxic than others, the differences being commonly ascribed to the hydrophobic nature of the variant. Microcystin-LR (MCLR) [X = l-leucine (L); Z = l-arginine (R); R1 = R2 = CH(3)] is the most toxic of all the microcystins investigated to date. This study investigates the similarity of the structures of MCLR and selected MC variants to the liver specific hormone vasopressin. Structures were compiled in HyperChem(®) (professional version 5.1). Initial comparisons of the MCLR and vasopressin indicated comparable volumes, surface areas and masses. Further studies using RMS overlays show that the microcystin derivative MCLR(Dha(7)) is comparably similar to vasopressin in terms of tertiary structure.

Selected cyclic dipeptides inhibit cancer cell growth and induce apoptosis in HT-29 colon cancer cells.

BACKGROUND: An increasing number of cyclic dipeptides (CDPs), particularly those containing proline, have been shown to exhibit important biological activity. MATERIALS AND METHODS: We investigated the potential of seven proline-based CDPs to inhibit cancer cell growth in HT-29, HeLa and MCF-7 cell lines. We also tested whether any of the CDPs were able to induce apoptosis in HT-29 cells. RESULTS: The SRB assay showed that only cyclo(Phe-Pro) (10 mM) exhibited more than 50% growth inhibition (p<0.01). The MTT assay was used to demonstrate a dose-dependent (0.008-10 mM) growth inhibition by cyclo(Phe-Pro). Hoechst 33342 staining showed that 5 mM cyclo(Phe-Pro) induced chromatin condensation in 18.3+/-2.8% (p<0.01) of HT-29 cells after 72 hours. Furthermore, annexin V binding revealed phosphatidylserine externalisation in cyclo(Phe-Pro)-treated HT-29 cells. CONCLUSION: Our findings demonstrate that cyclo(Phe-Pro) inhibits the growth of HT-29, MCF-7 and HeLa cells and induces apoptosis in HT-29 colon cancer cells, suggesting a potential antitumour activity.

The effect of the isomers of cyclo(Trp-Pro) on heart and ion-channel activity.

Cyclo(L-Trp-L-Pro) has shown potential for use in the treatment of cardiovascular dysfunction. The aim of the study was to determine the effects of the isomers of cyclo(Trp-Pro) - cyclo(L-Trp-L-Pro), cyclo(L-Trp-D-Pro), cyclo(D-Trp-L-Pro) and cyclo(D-Trp-D-Pro) - on heart and ion-channel activity. The effects on L-type Ca(2+)-channel, Na(+)-channel and inward rectifier K(+)-channel activity were determined by using the whole-cell patch-clamp technique on myocytes of guinea-pig origin. Dependence on the membrane potential in terms of Ca(2+)-channel activity was also investigated. A modified Langendorff method was used to determine the effects of the isomers on heart rate, coronary flow, duration of ventricular tachycardia and arrhythmia, time to sinus rhythm and QRS interval on the rat isolated heart. Cyclo(L-Trp-L-Pro), cyclo(L-Trp-D-Pro) and cyclo(D-Trp-D-Pro), 100 microM, showed agonism towards Ca(2+)-channel activity, while cyclo(D-Trp-L-Pro) caused a blockage of the current. The action of cyclo(D-Trp-L-Pro) was shown to be independent of membrane potential. No significant effect (P > 0.05) on the inward rectifier K(+) current was observed in the presence of cyclo(L-Trp-D-Pro) and cyclo(D-Trp-D-Pro), while antagonism was noted in the presence of cyclo(L-Trp-L-Pro) and cyclo(D-Trp-L-Pro). All isomers showed antagonist effects on the Na(+) channel. No adverse effects were noted on chronotropic effects in the presence of 200 microM cyclo(L-Trp-L-Pro) and cyclo(D-Trp-D-Pro) (P > 0.05), while cyclo(L-Trp-D-Pro) significantly increased the heart rate. Cyclo(D-Trp-L-Pro) significantly reduced the heart rate (P < 0.05). In addition, no significant effects were observed on the coronary flow rate in the presence of the isomers. All isomers significantly reduced the duration of ventricular tachycardia and arrhythmia, as well as the time to sinus rhythm. Furthermore, no change in the QRS intervals was noted in the presence of the isomers in comparison with the control, with a significant increase being noted for cyclo(D-Trp-D-Pro) (P < 0.05) in reference to the other isomers. The isomers thus show antiarrhythmic potential and may manifest as novel agents in the treatment of cardiovascular dysfunction, since a decrease in ventricular fibrillation may reduce the mortality rates in acute myocardial infarction.

Antidiabetic and cytotoxicity screening of five medicinal plants used by traditional African health practitioners in the Nelson Mandela Metropole, South Africa.

Diabetes mellitus is a growing problem in South Africa and of concern to traditional African health practitioners in the Nelson Mandela Metropole, because they experience a high incidence of diabetic cases in their practices. A collaborative research project with these practitioners focused on the screening of Bulbine frutescens, Ornithogalum longibracteatum, Ruta graveolens, Tarchonanthus camphoratus and Tulbaghia violacea for antidiabetic and cytotoxic potential. In vitro glucose utilisation assays with Chang liver cells and C2C12 muscle cells, and growth inhibition assays with Chang liver cells were conducted. The aqueous extracts of Bulbine frutescens (143.5%), Ornithogalum longibracteatum (131.9%) and Tarchonanthus camphoratus (131.5%) showed significant increased glucose utilisation activity in Chang liver cells. The ethanol extracts of Ruta graveolens (136.9%) and Tulbaghia violacea (140.5%) produced the highest increase in glucose utilisation in C2C12 muscle cells. The ethanol extract of Bulbine frutescens produced the most pronounced growth inhibition (33.3%) on Chang liver cells. These findings highlight the potential for the use of traditional remedies in the future for the management of diabetes and it is recommended that combinations of these plants be tested in future.